WASHINGTON — As the Pentagon and other federal agencies are expected to spend the remainder of their budgets before the end of the fiscal year Sept. 30, a bipartisan quartet of senators is urging federal agencies to explain how they will avoid waste and abuse.

Federal agencies reportedly spent more than $11 billion in the final week of fiscal year 2017, and a reported eight of the top ten highest-spending federal agencies have not used as much as 40 percent of their budgets, the lawmakers wrote to the chief financial officers of 13 federal agencies.

“Historically, federal agencies increase spending during the fourth quarter of the fiscal year. Although not a new phenomenon, use it or lose it spending can lead to waste and abuse of taxpayer dollars,” they said in the letter Wednesday to Pentagon Comptroller David Norquist. The letter requested a staff-level briefing.

The Pentagon received flexibility through the 2018 omnibus appropriations vehicle to spend up to 25 percent of its operations and maintenance budget in the last two months of the fiscal year — and added flexibility to reprogram funds. It amounts to legislative relief from the so-called “80/20 rule,” a statutory limitation that not more than 20 percent of one-year appropriations may be obligated during the last two months of the fiscal year.

The letter came from Sens. Ron Johnson, R-Wis., and Claire McCaskill, D-Mo., the respective chairman and ranking member of the Senate Homeland Security and Governmental Affairs Committee, and from Sen. Rand Paul, R-Ky., and Gary Peters, D-Mich., the respective chairman and ranking member of the panel’s Subcommittee on Federal Spending Oversight and Emergency Management.

The letters were sent to the CFOs of the Defense Department, Department of the Treasury, Department of Veterans Affairs, Department of Homeland Security, Department of Energy, Department of Justice, Department of State, Department of Transportation, Department of Health and Human Services, General Services Administration, NASA, National Science Foundation and Social Security Administration.